Goodgrouper, I hope I'm not too late for you to read this; but I too love 10X ! I got fantastic groups and speed in my 20TAC(driver) using 39gr. pills. By that, I mean 3892fps and groups consistently in the 3s. Out of an AR 15 ! One problem I found though that you should and may be aware of; it is very temp. sensitive. That's the only complaint I have and is easily overcome. I could put 25.1 gr. in it at 50 degrees; but had to drop to 24.1 at 70 degrees. As for my 223AI; I want to shoot 55gr. pills in my 14 twist barrel and I WILL try 10X ! My upper builder used to get 3650 fps with an Accurate powder. They changed it and now it only goes about 3400. Bummer. And it was danged accurate too ! His go to powder in the 20 TAC (driver) is 2460; it meters great and the same volume of it is equal to my 24.1 gr. of 10X with the same velocity and accuracy. You can bet if I try 10X, I'm going to try 2460 ! One other caveat; someone said 10X reformulated. It's true; the newer cans show the word"new" on them. All I found was it burns a whole lot cleaner. Good luck on your quest and I hope this is informative and not too late.

Load data is indeed scarce. For those situations I use QuickLoad - been using it a lot for 3+ years now. I use it to get in the ballpark, then back off 2 grains and work up.

Easy does it.

I think 27.5g is a pretty hot load - it is also a compressed load of close to 110% - I'd think you have to use a drop tube to get it in there. The QuickLoad model predicts about 4,000 fps out of a 24" barrel with a 27.5g load of RL10X which isn't that far off what you are measuring.

I'd estimate that load at between 7,500 and 10,000 psi over the SAAMI max (55,000 psi) for the brass based on a QuickLoad model optimized for my CZ527 American sporter (30.49 water grain case capacity - 2.272" COL). It may or may not show pressure signs. Bolt lift and primer pockets sometimes don't show up until one is way way over.

If you are at 65,000 psi @ 70F as I estimate, you are about 5,000 psi short of where you will get brass flow and rapid primer pocket expansion. Be advised on a hot day, say 110F, your pressure could easily exceed 70,000 psi.

At 25.5g I was getting around 3700 fps with RL10X. It didn't group well so I stopped experimenting with it.

There is no magic. Velocities of 200 to 300 fps over max loads with other good powders optimized for the bullet are only possible with excessive pressure.

As Ken Ohler once wrote, "any reloader can get velocities faster than factory ammo if they don't measure pressure."